1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition suitable as a chemically-amplified resist useful for microfabrication utilizing various types of radiation such as deep ultraviolet rays such as a KrF excimer laser, ArF excimer laser, and F2 excimer laser, X-rays such as synchrotron radiation, or charged particle beams such as electron beams.
2. Description of Background Art
In the field of microfabrication represented by the manufacture of integrated circuit devices, lithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in order to increase the degree of integration.
A conventional lithographic process utilizes near ultraviolet rays such as an i-line radiation. However, it is very difficult to perform microfabrication with a line width of sub-quarter micron using near ultraviolet rays.
Therefore, in order to enable microfabrication with a line width of 0.20 μm or less, utilization of radiation with a shorter wavelength has been studied. Deep ultraviolet rays represented by a bright line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given as radiation with a shorter wavelength. Of these, a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (wavelength: 193 nm) have attracted attention.
As a resist applicable to the excimer laser radiation, a number of resists utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a component generating an acid (hereinafter referred to as “photoacid generator”) which generates an acid upon irradiation (hereinafter referred to as “exposure”) have been proposed. Such a resist is hereinafter called a chemically-amplified resist.
Japanese Patent Publication No. 2-27660 discloses a chemically-amplified resist containing a polymer having a t-butyl ester group of a carboxylic acid or t-butyl carbonate group of a phenol and a photoacid generator. The t-butyl ester group or t-butyl carbonate group in the polymer dissociates by the action of an acid generated upon exposure, whereby the polymer has an acidic group such as a carboxylic group or a phenolic hydroxyl group. As a result, exposed areas of the resist film become readily soluble in an alkaline developer.
Generally, conventional chemically-amplified resists contain a phenol resin as a base resin. However, since deep ultraviolet rays used as radiation are absorbed due to the presence of aromatic ring in the resin, a sufficient amount of deep ultraviolet rays cannot reach a lower portion of the resist film. Therefore, the irradiation dose is increased in the upper portion of the resist film and decreased in the lower portion. As a result, the resist pattern after development is in the shape of a trapezoid in which the resist pattern is thinner in the upper portion and thicker in the lower portion, whereby sufficient resolution cannot be obtained. If the resist pattern after development is in the shape of a trapezoid, desired dimensional accuracy cannot be achieved in a succeeding step such as an etching step or ion implantation step. Moreover, if the shape of the upper part of the resist pattern is not rectangular, the rate of removal of the resist by dry etching is increased, whereby it is difficult to control etching conditions.
The shape of the resist pattern can be improved by increasing the radiation transmittance of the resist film. For example, a (meth)acrylate resin represented by polymethylmethacrylate is a highly desirable resin from the viewpoint of radiation transmittance, because the (meth) acrylate resin has high transparency to deep ultraviolet rays. Japanese Patent Application Laid-open No. 4-226461 discloses a chemically-amplified resist using a methacrylate resin, for example. However, this composition has insufficient dry etching resistance due to the absence of an aromatic ring, although the composition excels in microfabrication performance. This makes it difficult to perform etching with high accuracy. Therefore, a composition having both transparency to radiation and dry etching resistance cannot be provided.
As a means to improve dry etching resistance of the chemically-amplified resist without impairing transparency to radiation, a method of introducing an aliphatic ring into the resin component in the resist instead of an aromatic ring is known. For example, Japanese Patent Application Laid-open No. 7-234511 discloses a chemically-amplified resist using a (meth)acrylate resin having an aliphatic ring.
This resist uses a group which comparatively easily dissociates by the action of a conventional acid (acetal functional group such as a tetrahydropyranyl group), or a group which comparatively scarcely dissociates by the action of an acid (t-butyl functional group such as a t-butyl ester group or t-butyl carbonate group) as the acid-dissociable functional group in the resin component. However, in the case of using the resin component containing the former acid-dissociable functional group, although the resist excels in basic properties such as sensitivity and pattern shape, storage stability as a composition is insufficient. In the case of using the resin component containing the latter acid-dissociable functional group, the resist exhibits insufficient basic properties such as sensitivity and pattern shape, although storage stability as a composition is excellent. Moreover, since the aliphatic ring is introduced into the resin component in this resist, hydrophobicity of the resin is considerably increased. This results in insufficient adhesion to a substrate.
In view of development of technology capable of dealing with recent progress in microfabrication of integrated circuit devices, a chemically-amplified resist which is applicable to short wavelength radiation represented by deep ultraviolet rays, exhibits high radiation transmittance, and excels in basic characteristics as a resist such as sensitivity, resolution, dry etching resistance, and pattern shape has been strongly demanded.
An object of the present invention is to provide a radiation-sensitive resin composition suitably used as a chemically amplified resist having high transmittance of radiation and exhibiting superior basic properties as a resist such as sensitivity, resolution, dry etching resistance, and pattern shape.